Waste water disposal system

ABSTRACT

A system and method for injecting waste water into a disposal well comprising a plurality of horizontal tanks interconnected to one another in series in a way that fluid communication is established between the horizontal tanks. The tank chambers of the horizontal tanks collectively have a volume to accommodate a capacity of at least 6,000 barrels of waste water in a twenty-four hour period while providing the waste water sufficient retention time to permit water, oil, and solids to separate from one another.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional application Ser. No. 61/694,840 filed on Aug. 30, 2012, the entire contents of which being hereby expressly incorporated herein by reference.

BACKGROUND

Oil and gas production often produces large quantities of waste water at the site of the well bore. The waste water often has high salt content and may contaminate fresh water if allowed to drain into fresh water sources such as surface streams or ground water. Oil and gas producers may therefore desire, or be required to, dispose of waste water in a manner so as to attempt to avoid contamination of fresh water sources or damage the surrounding areas.

Disposing of waste water may be performed by draining the waste water into sumps or ponds, where the waste water evaporates or seeps into the subsoil. The waste water seeping into the subsoil may contaminate subsurface fresh water sources. Alternatively, waste water may be injected into wells such as those used for oil and gas production which no longer sustain suitable production levels. These wells, called injection wells, allow for injecting waste water below fresh water levels and collecting the waste water in formations below that of the fresh water level.

Prior to injecting waste water into an injection well, it is desirable to recover additional hydrocarbons from the waste water and to remove solids which might damage, or otherwise shorten the useful life of the injection well. Waste water separators used at injection well sites have historically employed one or more desanders and a series of vertical tanks through which the waste water is passed so as to cause water, hydrocarbons, and solids to separate from one another.

While vertical tanks have long been used in the oil and gas industry with a certain degree of effectiveness, significant amounts of oil nevertheless can remain entrained in the waste water, and thus, be injected down the injection well. With the ever increasing value of oil, there is a need for a waste water disposal system that more effectively separates oil from waste water prior to disposal of the waste water without reducing or interfering with the injection capacity of the injection well. It is to such a waste water disposal system that embodiments of the inventive concepts disclosed herein are directed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of a waste water disposal system constructed in accordance with the inventive concepts disclosed herein.

FIG. 2 is a partially cutaway, elevational view of an embodiment of a horizontal tank used in conjunction with the waste water disposal system of FIG. 1.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining at least one embodiment of the present inventive concepts in detail, it is to be understood that the presently disclosed inventive concepts are not limited in their application to the details of construction, experiments, exemplary data, and/or the arrangement of the components set forth in the following description or illustrated in the drawings. The presently disclosed inventive concepts are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for purpose of description and should not be regarded as limiting.

Referring now to FIG. 1, a waste water disposal system 100 for injecting waste water into an injection well, such as injection well 102, is illustrated. The waste water disposal system 100 utilizes a plurality of horizontal tanks 104 and a pump 106. The plurality of horizontal tanks 104 and the pump 106 are connected in series by a plurality of conduits 108. As will be described below, waste water is directed through the horizontal tanks 104 where water, oil, and solids are allowed to separate from one another. The water is in turn injected into the injection well 102 via the pump 106, and the oil and the solids may be periodically removed from the horizontal tanks 104, as desired.

Referring now to FIG. 2, each of the horizontal tanks 104 has a longitudinal axis which is in a horizontal orientation. The horizontal tanks 104 may be formed in a variety of shapes, such as cylindrical or rectangular, and may be constructed of any suitable material, such as polyethylene or other non-metallic or metallic materials, such that the horizontal tanks 104 are suited for containment of liquids which may be found in the production of hydrocarbons.

Each of the horizontal tanks 104 has a first end 110, a second end 112, and a sidewall 114 which cooperate with one another to define a tank chamber 116. Each of the horizontal tanks 104 is further characterized as having a length 118 extending between the first end 110 and the second end 112, a height 120, and a width 122 (FIG. 1). As will be further described below, the length 118 is greater than the height 120.

Each of the horizontal tanks 104 is provided with an inlet 124 and an outlet 126. The inlet 124 may be provided in the first end 110 and the outlet 126 may be provided in the second end 112 whereby waste water enters the tank chamber 116 at one end (e.g., the first end 110) of the horizontal tank 104 and exits the tank chamber 116 at the opposite end (e.g., the second end 112) of the horizontal tank 104. As will be described further below, the inlet 124 may be positioned in the first end 110 at a height substantially equal to the height of the outlet 126 in the second end 112. The position of the inlet 124 and outlet 126 may serve to limit formation of a stagnation layer in the waste water between the waste water and an oil layer formed on top of the waste water through gravity separation.

Each of the horizontal tanks 104 may be provided with a skimmer port 128 formed therein in communication with the tank chamber 116. The skimmer port 128 may have a cover 130 to seal the skimmer port 128 from introduction of foreign matter into the tank chamber 116. The cover 130 may be displaced to expose the tank chamber 116 and the contents of the tank chamber 116. Once the cover 130 is displaced, the oil layer formed on top of the waste water may be removed from the surface through suction, scraping, skimming or any other suitable method of manual or automatic removal of the oil layer.

Each of the horizontal tanks 104 may also be provided with one or more cleanout ports 132 to facilitate the removal of solids from the horizontal tanks 104. The cleanout ports 132 are desirably sealed in a fluid-impermeable way during the operation of the waste water disposal system 100, and may be used to permit access, cleaning, or maintenance, of the interior and internal components of the horizontal tanks 104.

The size of the horizontal tanks 104 can be varied. However, to accommodate a capacity of at least 6,000 barrels of waste water in a 24-hour period while providing adequate retention time to permit the water, oil, and solids to separate from one another, the horizontal tanks 104 may be dimensioned so that the length 118 of the horizontal tanks 104 is at least three times greater than the height 120 of the horizontal tanks 104, and more preferably about four times greater. By way of example, the horizontal tanks 104 may have a length 118 in a range from about 35 feet to about 45 feet, a height 120 in a range of from about 10 feet to about 15 feet, and a width 122 in a range from about 10 feet to about 15 feet. By way of further example, the inlet 124 and the outlet 126 may be positioned approximately 18 to 36 inches from the bottom of the horizontal tanks 104.

Each of the horizontal tanks 104 may be supported by a support structure 134. The support structure 134 may be implemented as a skid, as shown in FIG. 2. The support structure 134 serves as a footing for the horizontal tanks 104, eliminating the need for a permanent foundation. The support structure 134 enables the horizontal tanks 104 to be temporarily placed at a site of the injection well 102 for processing and disposal of waste water, and be removed after completion of waste water disposal, or upon the injection well 102 becoming unsatisfactory for disposal of waste water. Although shown in FIG. 2 as a skid, the support structure 134 may be implemented as a trailer, scaffolding, frame, or any other suitable structure or device capable of supporting one of the horizontal tanks 104 while allowing removal upon termination of the waste water disposal process. It will be appreciated, however, that the horizontal tanks 104 may be supported by a permanent structure as well, such as a concrete foundation.

As shown in FIG. 1, the horizontal tanks 104 are connected to one another in series with the conduits 108. The conduits 108 may be implemented as tubing, valves, hoses, combinations thereof, or other structures or combinations of structures which enable the horizontal tanks 104 to be connected to one another in fluid communication. To connect the horizontal tanks 104 in series, the outlet 126 of one of the horizontal tanks 104 is connected to the inlet 124 of another horizontal tank 104. While the waste water disposal system 100 is illustrated in FIG. 1 as having ten horizontal tanks 104, it should be understood that the number of horizontal tanks 104 employed may be varied depending on the injection capacity of the injection well 102, desired retention time, and the size of the horizontal tanks 104.

As shown in FIG. 1, one or more desanders 136 may be employed prior to the initial horizontal tank 104 to remove a portion of aggregate such as sand, mud, gravel, and other solids from the waste water prior to the waste water being introduced into the initial horizontal tank 104.

In operation, waste water may be introduced to the waste water disposal system 100 via a transport vehicle 138 which is used to transport waste water to the waste water disposal site. The transport vehicle 138 connects to a fluid inlet conduit 108 a and discharges waste water into the fluid inlet conduit 108 a thereby initiating fluid flow into the desander 136. It will be appreciated that the waste water disposal system 100 may be arranged so that more than one transport vehicle 138 may discharge waste water into waste water disposal system 100 at the same time.

After passing through the desander 136, waste water enters the first horizontal tank 104 through the inlet 124, and fills the tank chamber 116 to the height of an outlet 126. As waste water continues to fill the tank chamber 116 past the height of the outlet 126, waste water passes through the outlet 126 of the first horizontal tank 104 and passes to the subsequent horizontal tank 104. The outlet 126 is sized relative to the inlet 124 to restrict the flow of liquid through the horizontal tank 104 such that the liquid level remains a distance above the outlet 126 to prevent oil which separates from the waste water from passing from the horizontal tank 104. Also, the restriction of the fluid creates the desired retention time for the waste water. The retention time of the waste water allows for gravity separation of solids and hydrocarbons, such as oil, from the waste water. During the initial gravity separation, the hydrocarbons form a layer at the top of the waste water, above the height of the outlet 126. Although the liquid level will vary during operation, it is desirable to maintain the liquid level at a height that is at or near an intermediate height of the horizontal tank 104 to maximize the horizontal surface area of the liquid.

To control the height of liquid (e.g., the height of waste water inside the tank chamber 116), the initial horizontal tank 104 may be provided with a liquid level sensor 140, such as a float, which in turn may be used to control a valve 142. The liquid level sensor 140 is positioned in the horizontal tank 104 at a predetermined high level position. When the liquid reaches the high level, the liquid level sensor 140 causes a valve 142 to close thereby terminating the flow of liquid into the initial horizontal tank 104. Upon the liquid level in the initial horizontal tank 104 falling to a desired level, the valve 142 is caused to open.

Similarly, the last horizontal tank 104 may be provided with a liquid level sensor 144, such as a float, which in turn may be used to control a valve 146 interposed in a discharge conduit 147. The liquid level sensor 144 is positioned in the last horizontal tank 104 at a predetermined low level position. When the liquid reaches the low level, the liquid level sensor causes the valve 146 to close thereby terminating the flow of liquid from the last horizontal tank 104. A high level sensor 148 may be used to open the valve 146 upon the liquid in the last horizontal tank 104 rising to a predetermined level.

The waste water continues to pass through each subsequent horizontal tank 104 until the waste water exits the last horizontal tank 104 and is injected into and down the injection well 102 via the pump 106.

While waste water is flowing through the plurality of horizontal tanks 104, the oil layer formed by gravity separation may be removed through the skimmer port 128. The oil layer may be removed using a suction device or manual skimming device inserted through the skimmer port 128. The skimmer port 128 may also be used to introduce surfactants into the waste water by injecting the surfactant into the waste water, below the oil layer, via tubing (not shown). The surfactant may also be introduced before or during introduction of the waste water to the waste water disposal system 100 by injecting the surfactant through the inlet 124.

From the above description, it is clear that the inventive concepts disclosed herein are well adapted to carry out the objects and to attain the advantages mentioned herein, as well as those inherent in the inventive concepts disclosed herein. While exemplary embodiments of the inventive concepts have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the inventive concepts disclosed. 

What is claimed is:
 1. A system for injecting waste water into a disposal well, comprising: a plurality of horizontal tanks, each of the horizontal tanks has a first end, a second end, and a sidewall which cooperate with one another to define a tank chamber, each of the horizontal tanks further has a length extending from the first end to the second end, a height, and a width with the length being greater than the height, the horizontal tanks being interconnected to one another in series in a way that fluid communication is established between one of the first end and the second end of the horizontal tanks and one of the first end and the second end of an adjacent one of the horizontal tanks and in a way that one of the horizontal tanks is defined as an initial horizontal tank and one of the horizontal tanks is defined as a final horizontal tank; a fluid supply conduit connected to the initial horizontal tank so as to permit waste water containing a mixture of water, oil, and solids to be received by the fluid supply conduit and passed into the initial horizontal tank; a fluid discharge conduit connected to the discharge horizontal tank so as to enable the waste water that has passed through each of the horizontal tanks to be discharged from the discharge horizontal tank and into the fluid discharge conduit; and a pump operably interposed in the discharge conduit to force fluid that passes through the horizontal tanks into the disposal well, wherein the tank chambers of the horizontal tanks collectively have a volume to accommodate a capacity of at least 6,000 barrels of waste water in a twenty-four hour period while providing the waste water sufficient retention time to permit water, oil, and solids to separate from one another.
 2. The system of claim 1, wherein the length of each of the horizontal tanks is at least about out three times greater than the height.
 3. The system of claim 1, wherein each of the horizontal tanks is supported by a skid.
 4. The system of claim 1, wherein each of the horizontal tanks has an inlet formed in the first end and an outlet formed in the second end, and wherein the inlet is positioned in the first end at a height substantially equal to the height of the outlet in the second end.
 5. The system of claim 4, wherein the inlet and the outlet are positioned approximately 18 to 36 inches from a bottom of the horizontal tanks.
 6. The system of claim 4, wherein the outlet is sized relative to the inlet to restrict the flow of liquid through the horizontal tank such that the liquid level remains a distance above the outlet to prevent oil which separates from the waste water from passing from the horizontal tank.
 7. The system of claim 1, wherein the length of each of the horizontal tanks is in a range from about 35 feet to about 45 feet, the height is in a range from about 10 feet to about 15 feet, and the width in a range from about 10 feet to about 15 feet.
 8. A method for separating hydrocarbons and solids from waste water to be injected in a disposal well, comprising: introducing a volume of waste water containing water, hydrocarbons, and solids into a series of horizontal tanks, each of the horizontal tanks having a first end with an inlet, a second end with an outlet, and a sidewall which cooperate with one another to define a tank chamber, each of the horizontal tanks further has a length extending from the first end to the second end, a height, and a width with the length being greater than the height, the horizontal tanks being interconnected to one another in series in a way that fluid communication is established between one of the first end and the second end of the horizontal tanks and one of the first end and the second end of an adjacent one of the horizontal tanks and in a way that one of the horizontal tanks is defined as an initial horizontal tank and one of the horizontal tanks is defined as a final horizontal tank; flowing the waste water through series of horizontal tanks at a rate which fills each of the tank chambers to a height greater than the outlet such that the liquid level in the horizontal tanks remains a distance above the outlet to prevent oil which separates from the waste water from passing from the horizontal; withdrawing a volume of water from the discharge horizontal tank; and injecting the withdrawn volume of water into the injection well.
 9. The method of claim 8, wherein the tank chambers of the horizontal tanks are collectively provided with a volume to accommodate a capacity of at least 6,000 barrels of waste water in a twenty-four hour period while providing the waste water sufficient retention time to permit water, oil, and solids to separate from one another.
 10. The method of claim 8, further comprising the step of to maintaining the liquid level in the horizontal tanks at a height that is at or near an intermediate height of the horizontal tank to maximize the horizontal surface area of the liquid. 